A < B Comparisons using TTL logic

Thread Starter

Enliten

Joined Feb 10, 2009
17
Im sure im being stupid, but give i have 12bit data line, whats the best way of being able to see if the binary value is < different values (in TTL)- such as 96, I could use lots of different TTL comparators but there are about 8 different values, seems like alot of comparators?

Thanks


Adrian
 

Thread Starter

Enliten

Joined Feb 10, 2009
17
What im looking at doing might not be possible. Basically im trying to produce a simple vga test signal (just a couple of coloured bars) using a 25.175 crystal and some TTL. Am I wasting my tme? I know a CPLD or FPGA would probably be better but hey - its a challange ;)
 

kubeek

Joined Sep 20, 2005
5,587
Not sure how complex the VGA signal is, but everything is possible. But one of the possible outcomes is an A4 double-sided board :)
 

Thread Starter

Enliten

Joined Feb 10, 2009
17
Yes, thats true - everything is possible. Need to get myself a nice osc. scope though to see if it works at 25mhz ;)
 

kubeek

Joined Sep 20, 2005
5,587
If you want to see the comparison of two parallel 12-bit words, logic analyzer is a better idea. Isn´t there some ready proven circuit on the almighty Internet that you could use, instead of building it from a scratch?
 

Thread Starter

Enliten

Joined Feb 10, 2009
17
I realised that with a bit of lateral thinking i could simplify the problem to 8bit comparisons which could be done using some 688 chips. This was possible as the sync signal while needing 25mhz clock and a count of up to 800 can be divided by 16 so i use a 4 bit counter to reduce the clock down before passing the circuit on :)
 
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